Cross-wind bobbin

ABSTRACT

In a cross-wound bobbin ( 1 ), the helical lines along which the yarn ( 4 ) is wound have a different inclination in adjacent layers. The winding ratios are selected such that the quantity drawn off is greater if the unwinding point is moving from the unwinding end to the bottom end, compared to the quantity drawn off if the unwinding point is moving from the bottom end to the unwinding end.

DETAILED DESCRIPTION OF THE INVENTION

[0001]FIG. 1 schematically illustrates the conditions involved inunwinding a known cross-wound bobbin 1. The cross-wound bobbin 1comprises a cheese cone 2, which is wound onto a tubular bobbin tube 3.A thread or yarn 4 forms the cheese cone 2. The yarn 4 is wound inlayers of windings with the aid of a known traversing device. Two ofthese layers are shown schematically and in part. The yarn is indicatedin one layer by reference numeral 5 and in the other layer by referencenumeral 6. For instance, let layer 5 be the layer or winding locatedfarther inward, while the layer 6 or winding is located radially fartheroutward. In one layer, such as layer 5, the windings of the yarn 4 forma counterclockwise helix, while in the windings of yarn in layer 6 forma clockwise helix. The angles of inclination at which the yarn 5 iswound are quantitatively relatively large, compared to a plane 7 locatedperpendicular to the longitudinal axis of the bobbin tube 3. That is,the height of inclination of the helixes that the layers 5 and 6 form ismultiple times larger than the thickness of the yarn 4. In this way, thewindings of one layer are prevented from being able to force their wayinto the other layer and forcing the windings of that layer apart.

[0002] The cross-wound bobbin 1 obtained in this way forms an unwindingend 8 that is an essentially plane annular face. Turning points 9, wherethe yarn course changes from one layer to the next and thus from onehelical line to the helical line in the opposite direction, are locatedin the region of the unwinding end. The turning points 9 in the regionof the unwinding end are distributed as randomly as possible, or morespecifically are randomly distributed in both the circumferentialdirection and, with a certain range of deviation, in the axialdirection. These provisions are intended on the one hand to attaineffective stabilization of the unwinding end and on the other to avertan agglomeration of material.

[0003] The foot end is located on the other axial end of the cross-woundbobbin 1 and is built up in the same way as the unwinding end 8 that canbe seen in FIG. 1.

[0004] From the outer circumferential surface of the cross-wound bobbin1, the yarn 4 is drawn off through an eye 11, which is axially spacedapart from the cross-wound bobbin 1 and is located on the axis ofsymmetry. The yarn eye 11 is fixed in space. The cross-wound bobbin 1 islikewise unmoving while the yarn is being drawn off.

[0005] Because of the adhesion of the yarn to the effective surface ofthe bobbin, a defined unwinding point 12 develops, beyond which thecourse of the yarn, in the travel direction of the yarn 4 duringunwinding, no longer corresponds to the yarn course inside thecross-wound bobbin 1. The unwinding point 12 circulates in thecircumferential direction along the helical line that the yarn 4 formson the outside of the cheese cone 2 at the time, and at the same timethe unwinding point 12 moves in the longitudinal direction of thecross-wound bobbin 1.

[0006] The speed at which the unwinding point 12 circulates in thecircumferential direction, or in other words its angular speed, dependson the yarn unwinding speed and on the diameter of the cheese cone 2.The greater the diameter of the cheese cone 2 and the lower theunwinding speed, the lower is the angular speed at which the unwindingpoint 12 rotates. Conversely, the angular speed increases if, at aconstant unwinding speed, the winding diameter has decreased because ofincreasing yarn consumption.

[0007] Because the unwinding point 12 rotates about the circumference ofthe cheese cone 2, the yarn segment between the yarn eye 11 and theunwinding point 12 rotates about the imaginary axis that is defined bythe yarn eye 11 and the axis of symmetry of the cheese cone 2. Therotation generates a centrifugal force that tends to push the drawn-offlength of yarn radially outward.

[0008] While the cheese cone is still full, the circulation speed of theunwinding point 12 of the yarn 4 from the top end of the cheese cone 2,for a given yarn consumption rate, is still relatively slight. Theincident centrifugal force is insufficient to unwind the yarn 4,immediately adjacent to the unwinding point 12, from the top end of thecheese cone 2. On the far side of the unwinding point 12, the yarn 3will first slide over the top end of the cheese cone 2, before reachingopen spec after moving past the unwinding end 8.

[0009] In space, the freely floating length of yarn defines a surface ofrevolution whose apex is located at the yarn eye 11. The generatrix ofthis surface of revolution is the freely floating length of yarn itself,which describes a complicated three-dimensional curve. This freelyfloating length of yarn is engaged not only by centrifugal force butalso by air resistance, so the yarn course is not a simple line locatedin one plane. The volume defined by the freely floating length of yarnis known as a yarn balloon.

[0010] As consumption increases, the outer diameter of the cheese cone 2decreases. Since the yarn unwinding speed remains constant, theunwinding point 12 must circulate faster, to compensate for thereduction in yarn length along the circumference that is due to thereduction in diameter.

[0011] Beyond a certain angular speed, the centrifugal force will behigh enough to lift the yarn 4 from the top end of the cheese cone 2immediately adjacent to the unwinding point 12.

[0012] The adhesion of the yarn 4 to the layers of yarn beneath it,irregularities in the air resistance of the yarn caused by structuralchanges, fluctuations in yarn tension, and still other such factors,mean that in a range of angular speed of the unwinding point 12, theunwinding conditions will constantly alternate between sliding on thesurface of the cheese cone 2 and floating above the surface. Theinventors have determined that this alternation back and forth betweenthe two unwinding situations is also influenced by whether the unwindingpoint 12 is moving away from the unwinding end 8, or toward theunwinding end 8.

[0013] If the unwinding point 12 is moving away from the unwinding end8, the circulation speed and thus also the centrifugal force increase,resulting in a tendency for the yarn 4 immediately adjacent to theunwinding point 12 to come loose from the top end of the cheese cone 2and float freely above the surface. Conversely, if the unwinding point12 is moving toward the unwinding end 8, the circulation speed and thecentrifugal force decrease, so that the yarn 4 instead has the tendencyto slip over the top end.

[0014] The effects of air resistance on the top end of the cheese cone 2will also have a corresponding influence in this respect.

[0015] Not until the angular speed of the unwinding point has increasedstill further will a changeover to the unwinding situation in which theyarn slides above the surface no longer occur.

[0016] The progressive yarn consumption causes the diameter of thecheese cone 2 to shrink increasingly and causes the angular speed of theunwinding point 12 to increase further. The greater speed of the yarn inthe air causes the single balloon that initially forms to become aso-called double balloon, with two clearly recognizable balloon portionsjoined to one another by a narrow constriction. The course of thefloating length of yarn in this situation is shown in FIG. 2.

[0017] The transition from the situation shown in FIG. 1 to thesituation shown in FIG. 2 likewise takes place in a range in which thereis constant alternation between the conformation of FIG. 1 and theconformation of FIG. 2. Not until beyond a certain angular speed willthe conformation of FIG. 2 develop exclusively.

[0018] At a very low package diameter, finally, a triple yarn balloon iscreated, with two recognizable constrictions. The yarn course associatedwith this triple balloon is shown in FIG. 3. The transition from theconformation of FIG. 2 to the conformation of FIG. 3 also extends overan angular speed range in which the balloon alternates constantlybetween being double and triple. Different forces and yarn tensions thatoccur in the yarn are certainly associated with the various types ofballoon.

[0019] The strength of a yarn has a bell-curve distribution around amean tensile strength value. Because of the deviation in the strengthvalues, there are some segments in the yarn that have a markedly higherbreaking strength and conversely other segments that already break atmarkedly lesser forces.

[0020] In turn, the yarn-using apparatus certainly does not generate asingle constant force; on the contrary, its force will also bedistributed in a bell curve. Yarn breaks are to be expected in the rangein which the gaussian curve of the force that actually occurs overlapsthe strength distribution of the yarn, or in other words, the range inwhich the two gaussian curves overlap. The larger the area of overlap,the greater the likelihood that the yarn will break on the yarn-usingside, which accordingly leads to machine down times.

[0021] One quite critical place that the yarn must travel through fromthe cross-wound bobbin to the finished textile article is the unwindingfrom the lp 1 itself.

[0022]FIG. 4 shows the course of yarn tension, plotted over the packagediameter of the cross-wound bobbin 1. The unit of measurement for thepackage diameter is millimeters, and the unit of measurement for thetensile force is cN (grams). A severely zigzagging upper curve 13represents the course of the maximum incident force, in each case per100 measured values. Below it is a dark-colored tubular or bandlikerange 13, which represents the statistical standard deviation in themeasured tensile force values. The statistical mean value of theincident tensile force is located approximately in the middle of thisband. The graph is divided longitudinally into zones, numbered from 1 to6.

[0023] The unwinding of the yarn 4 from the cross-wound bobbin 1 beginsat the maximum diameter of the cross-wound bobbin if approximately 280mm. At this diameter, the angular speed of the unwinding point 12 is toolow for the centrifugal force to cause the yarn to come loose from thetop end of the cross-wound bobbin 1 directly at the unwinding point 12.In this operating situation, the yarn 4 slides over the surface andgenerates comparatively quite high maximum tensile stresses, even thoughthe mean value is relatively low, and the standard deviation is notexcessively high either, as the band 14 shows. The high maximum tensilestresses are due above all to the fact that the yarn 4 that is slidingon the surface catches on the yarn over which it is sliding, since theyarn surface itself is not smooth. Individual fibers protrude from it.

[0024] The operating situation in which the yarn slides persists in itspure form until a package diameter of approximately 260 mm.

[0025] Below about 260 mm, that is, at the transition between the zonesmarked 1 and 2 in the graph, the unwinding situation in which the yarn 4comes loose from the top end immediately adjacent to the unwinding point12 will sporadically occur. In the ranges in which the balloon hasalready formed from the unwinding point 12 on, the maximum unwindingforce drops abruptly, and then immediately rises again once the balloonforms, which is only adjacent to the unwinding end 7. In zone 2, verygreat fluctuations in the maximum unwinding force and also relativelygreat fluctuations in the range of the standard deviation can thereforebe observed.

[0026] As the diameter reduction progresses further, or in other wordsto the right of zone 2, the balloon adjacent to the unwinding point 12remains stable. Unwinding with sliding no longer occurs. The maximumincident tensile force decreases abruptly. The standard deviationbecomes less, and the mean value also drops. Clearly, to the right ofzone 2, the yarn 4 being unwound is mechanically much less heavilyloaded. The likelihood of yarn breakage is reduced significantly.

[0027] Down to a diameter of about 160 mm, that is, within zone 3,conditions remain stable, and the yarn tension rises only slowly. Theincrease in yarn tension can be ascribed to the higher rotational speedand the attendant greater load from air resistance and the greater massof yarn located in the balloon.

[0028] To the right of zone 3, a pronounced increase in the maximumtensile tress and also in the mean value can be observed. The balloonnow assumes even greater dimensions, which lead to higher tensilestresses because of higher centrifugal force. A randomly distributedalternation between the single balloon and the double balloon alsooccurs. Toward the end of zone 4, finally, the situation finallyswitches over in favor of the double balloon, whereupon the centrifugalforces abruptly drop, and hence so do the tensile stresses. Both thestandard deviation and the maximum stresses that occur, that is, theexceptional stresses in the direction of very high values, also decreaseabruptly. At the end of zone 5, at a diameter of less than 60 mm,finally, a change to a triple balloon can be observed. At the end ofzone 5, the maximum force again rises relatively sharply, and thenabruptly collapses, once the triple balloon has developed to a steadystate.

[0029] With the above as the point of departure, it is the object of theinvention to create a cross-wound bobbin that is suitable forquantitatively reducing the maximum tensile stresses that occur in theyarn and/or limiting them to a reduced operating range, in order tolessen the likelihood of yarn breakage.

[0030] In the cross-wound bobbin of the invention, the individual layersare wound with a different inclination of the helical lines. They arewound in such a way that the yarn length drawing off is greater if theunwinding point is moving from the unwinding end to the bottom end,compared to the yarn length that is drawn off if the unwinding point ismoving from the bottom end to the unwinding end. In other words, thehelix along which the unwinding point moves from the top end to thebottom end has a markedly lesser inclination than the helical line alongwhich the unwinding point moves from the bottom end toward the top end.Because of this provision, the unfavorable influence on the balloon thatis due to the fact that the unwinding point moves away from the yarnballoon at relatively high speed, can be reduced. Because of the lesserinclination of the helical line as the unwinding point moves away fromthe balloon, the axial speed of the unwinding point away from theballoon is reduced markedly, and the unfavorable influence on theballoon formation is lessened.

[0031] At smaller diameters, the cross-wound bobbin of the inventionshows the transition to the double balloon more clearly, which asexplained above is more favorable in terms of the maximum incidentstress. Once again, the diameter range over which switching back andforth between the single and the double balloon occurs is reducedmarkedly. Smaller ranges correspondingly lessen the likelihood of yarnbreakage.

[0032] If sliding unwinding occurs, the constant fluctuation betweensliding yarn unwinding and freely floating yarn unwinding in thecross-wound bobbin of the invention is reduced to a very much smallerdiameter range.

[0033] Compared with the prior art, a steady floating balloon thatbegins at the unwinding point will already develop at very much greaterouter diameters of the cheese cone.

[0034] In both cases, the invention makes a higher unwinding speedpossible.

[0035] By a suitable free choice of the pitch traverses of the helicallines within the cheese cone, it is possible within certain limits tocontrol when the switchover to the respectively other type of unwindingor conformation of the balloon occurs, or in other words when the changefrom the sliding unwinding to the free-floating unwinding after theunwinding point irreversibly occurs, or when the double balloon or thetriple balloon irreversibly occurs.

[0036] In FIG. 5, the cross-wound bobbin 1 of the invention is shownhighly schematically.

[0037] The cross-wound bobbin 1 of the invention has the same basicmakeup as the cross-wound bobbin 1 of the prior art. It has a bobbintube 3 on which the cheese cone 2 is applied. The course of the yarn onthe top end of the cheese cone 2 is shown schematically. In unwinding,the indicated takeoff point 12 moves in the upper visible yarn layer inthe direction of an arrow 15 from the bottom end 16 to the unwinding endor top end 8. The layer forms a clockwise helix. As soon as the uppervisible layer has been removed, the unwinding point 12 changes to thelayer beneath it, where the unwinding point 12′ (with a prime, becauseit is located in the next layer) moves in the direction of the arrow 17.This layer contains the yarn 4 in a counterclockwise helix.

[0038] As FIG. 5 clearly shows, the unwinding point 12′ completes 2.5revolutions when it moves from the top end or unwinding end 8 to thebottom end 16, but only about one revolution in moving from the bottomend 16 to the unwinding end 8. The winding ratio, in the instance shown,would be 1 to 2.5. In a departure from the winding ratio shown, stillother winding ratios up to 1:10 and preferably 1:5 are conceivable, anddepending on the yarn conditions they result in improved values for theunwinding force, compared with cross-wound bobbin in which the windingratio in the successive layers is 1:1. The term “winding ratio” isunderstood here to mean the number of windings in which the yarn iswound on along the way from the bottom end to the unwinding end, inproportion to the number of windings that the yarn describes on the tripin reverse.

[0039] In other words, the amount of the angle α that the yarn 4 in thelayer with the clockwise helix forms with the plane 7 is greater thanthe amount of the angle β that the yarn 4 in the layer with thecounterclockwise helix forms with the yarn 7.

[0040] Aside from the difference noted, the cross-wound bobbin 1 of FIG.5 is produced on the same criteria as usual. Agglomerations of materialare to be avoided, and to do so, the turning point 9 both at theunwinding end 8 and at the bottom end 16 is shifted. As random anorientation of the yarn course as possible, relative to the next layerhaving the same winding direction, is also sought, in order to avoidmoiré effects or regularities that cause problems.

[0041] Besides the conical shape as shown in FIG. 5, the cross-woundbobbin 1 can also be shaped, by means of suitable winding, in such a waythat its cone angle varies as a function of diameter, or that forinstance toward the end, i.e. at small diameters, it changes to acylindrical shape. It would also be conceivable to create a cross-woundbobbin 1 in which the cheese cone 2, adjacent to the unwinding end 8, isinitially cylindrical and then changes to a region where it isfrustoconical. A hyperboloid is thus approximated.

[0042] The cheese cone can also be cylindrical over the full length andthrough all diameters, as is conventional today.

[0043] Findings from a series of experiments demonstrate that theimprovement can be shown in table form as follows for the diameter of100 mm: Pitch ratio 1:1 Prior art 1:2 1:2.5 1:3 Maximum force 25 cN 18cN 11 cN 17 cN Standard deviation ±5 cN ±4 cN ±3 cN ±4 cN Mean value  6cN  5 cN  3 cN  5 cN

[0044] For a package diameter of approximately 65 mm, the followingrelationships pertain: Pitch ratio 1:1 Prior art 1:2 1:2.5 1:3 Maximumforce 35 cN 18 cN 15 cN 12 cN Standard deviation ±6 cN ±4 cN ±3 cN ±3 cNMean value  7 cN  4 cN  4 cN  2 cN

[0045] The angles of inclination α and β can be constant, with theexception of the peripheral regions at the unwinding end 8 and thebottom end 6. However, they can also vary over the axial length, andthey can furthermore be dependent on the radial spacing. Finally, it isconceivable to create a conical angle that increases up to the pointwhere the bobbin is full, by providing windings in the interior of thecheese cone, relative to the radial width, that do not have the fullaxial length; that is, windings are generated that beginning forinstance at the bottom end 16 reach only approximately halfway up thecheese cone 2.

[0046] The particular shape and angular ratio selected must beascertained individually by experimentation, because in the process ofunwinding the yarn, the type of yarn and the yarn material as well asthe yarn diameter all have a very substantial role. Optimization bymeans of a series of experiments is therefore unavoidable.

[0047] In a cross-wound bobbin, the helical lines in which the yarn iswound up have a different inclination in adjacent layers. The windingradios are selected such that the quantity drawn off is greater if theunwinding point is moving from the unwinding end to the bottom end,compared to the quantity drawn off if the unwinding point is moving fromthe bottom end to the unwinding end.

1. A cross-wound bobbin (1), having a bobbin core and having a cheesecone (2) which is made up of yarn (4) that is applied in layers to thebobbin core (3) and which has an unwinding end (8), from which the yarncan be drawn off overend, and a bottom end 16, wherein the yarn (4) inthe cheese cone (2) extends along a helical line from the unwinding end(8) to the bottom end (16) and in another helical line in the oppositewinding direction from the bottom end 16) to the unwinding end (8), andthe inclinations of the helical lines differ from one another such that,at least in one region of the cheese cone (2), the yarn length beingunwound in this region is greater if the unwinding point (12, 12′) ofthe yarn (4) on the outside of the cheese cone (2) has moved from theunwinding end to the bottom end (16), relative to the yarn length thatis drawn off in this region if the unwinding point (12, 12′) has movedfrom the bottom end (16) to the unwinding end (8).
 2. The cross-woundbobbin of claim 1, characterized in that the region is a region thatextends from a first diameter to a second diameter.
 3. The cross-woundbobbin of claim 1, characterized in that the region is a region thatextends from a first point to a second point that is axially spacedapart from the first point.
 4. The cross-wound bobbin of claim 1,characterized in that there is at least one further region, whichcontains a different winding ratio in accordance with claim
 1. 5. Thecross-wound bobbin of claim 1, characterized in that the bobbin core (3)is formed by a bobbin tube.
 6. The cross-wound bobbin of claim 1,characterized in that the cheese cone (2) is free of any coverings onthe unwinding end (8).
 7. The cross-wound bobbin of claim 1,characterized in that one yarn layer changes over to the next yarn layerat a turning point (9), and neither at the bottom end (16) nor at theunwinding end (8) are successive turning points (9) located directly oneabove the other.
 8. The cross-wound bobbin of claim 7, characterized inthat the turning points (9) are offset from one another in thecircumferential direction and/or in the longitudinal direction relativeto the axis of the cheese cone (2).
 9. The cross-wound bobbin of claim1, characterized in that the cheese cone (2) is shaped such that onsuccessive layers, moiré patterns do not develop.
 10. The cross-woundbobbin of claim 1, characterized in that the cheese cone (2), at leastof the full cross-wound bobbin (1), is cylindrical.
 11. The cross-woundbobbin of claim 10, characterized in that the cheese cone (2) iscylindrical over the entire operating range.
 12. The cross-wound bobbinof claim 1, characterized in that the cheese cone (2), at least of thefull cross-wound bobbin (1), tapers conically toward the unwinding end(8).
 13. The cross-wound bobbin of claim 1, characterized in that thecheese cone (2) is shaped such that the full cross-wound bobbin (1)forms a conical cheese cone (2), whose shape, with increasing yarnremoval, changes over to the cylindrical shape.
 14. The cross-woundbobbin of claim 1, characterized in that the yarn belongs to a groupwhich includes spun yarn, monofilament yarn, multifilament yarns, andtwisted yarns made from them.
 15. The cross-wound bobbin of claim 1,characterized in that the yarn is a yarn for textile or textile-industryuse.
 16. The cross-wound bobbin of claim 1, characterized in that theangle (α, β) at which the yarn (4) is wound in one yarn layer isquantitatively between 30° and 12°, in each case measured relative to aplane (7) that is perpendicular to the axis of the cheese cone (2), andthat the angle (α, β) at which the yarn (4) is wound in the other yarnlayer is quantitatively between 0.5° and 15°, measured relative to thesame plane (7).
 17. The cross-wound bobbin of claim 1, characterized inthat the winding ratio between winding from the bottom end (16) to theunwinding end (8) and winding from the unwinding end (8) to the bottomend (16) is between 1:1.2 and 1:10, and preferably between 1:1.5 and1:8.
 18. The cross-wound bobbin of claim 1, characterized in that thecheese cone is frustoconical in shape on the unwinding end (8) and/or onthe bottom end (16).